1. Field of the Invention
The present invention relates to the formation of passivating films of chromium oxide.
2. Prior Art
Techniques for forming an oxide layer on chromium (hereinafter often referred to as passivating) are known, and include the oxidation of bulk chromium and chromium thin films at temperatures above 650.degree.C in oxygen and in impure nitrogen, the initial interaction of chromium thin films and oxygen at temperatures of from -196.degree. to 300.degree.C at a pressure of about 10.sup..sup.-10 torr and the oxidation of chromium/copper films at 525.degree.C in forming gas. See, e.g.,
C. a. phalnikar, E. B. Evans and W. M. Baldwin, Jr. J. Electrochem. Soc. 103, 429-438 (1956); PA1 V. i. arkharov, V. N. Konev, I. Sh. Trakhtenberg and S. V. Shumilina Fig. Metal Metalloved., 5, 190-193 (1957); PA1 D. v. ignatov and R. D. Shamgunova N.A.S.A. Technical Translation F-59, 61-68 (1959); PA1 E. a. gulbransen and K. F. Andrew J. Electrochem Soc. 104, 334-336 (1957); PA1 A. u. seabolt, J. Electrochem. Soc. 107, 147-148 (1960); PA1 W. c. hagel, Trans. ASM 56, 583-599 (1963); PA1 R. a. rapp in Reactions between Gases and Solids, AGARD Conference Proceedings No. 52, Technical Editing and Reproduction Ltd., Harford House, 7-9 Charlotte St., London (1970); PA1 O. kubaschewski and B. E. Hopkins "Oxidation of Metals and Alloys" Acad. Press, New York (1953); PA1 R. e. grace and T. F. Kassner Acta Metallurgica 18, 247 (1970); and PA1 W. a. crossland and H. T. Roettgers, Physics of Failure in Electronics Vol. 5, Ed. T. S. Shilliday et al., Batelle Memorial Int., Columbus, Ohio, Clearing House for Fed. Sci. and Tech. Inf. (1967).
All of the above processes, however, suffer from the fault that they are not easily integrated into the thermal cycles of an already existing process, and generally have to be performed separately from the thermal cycles already existent in the process.
For example, processes for forming gas panel display devices often involve a high temperature thermal cycling step where metallurgy-glass assemblies are subjected to elevated temperatures sufficient to cause the glass to fuse and reflow. A gas panel display device fabrication process involving such a glass reflow step is described in U.S. Pat. No. 3,634,720 to Kupsky.
Known non-thermal techniques for forming a chromium oxide layer on chromium include wet chemical oxidations, anodic oxidations, and the deposition of chromium oxide by a spin drying method. It will be apparent that these procedures cannot easily be integrated with the thermal cycles of an already existent process.